This invention relates to balanced data transmission lines and, more particularly, to a bi-directional signal coupler for use therewith.
Data bus systems are well known and commonly used to connect a plurality of peripheral devices for communication between the devices and/or a central control unit. Such data bus systems can either be of the unbalanced or balanced type. In a typical unbalanced bus system, a single wire connects all of the peripheral devices and the central control unit. Data signals travel along the single wire, with the common ground of the system providing the return path. In a typical balanced bus system, there are two wires with one of the wires carrying the data signals and the other wire providing the return path. The present invention is concerned with such a two wire balanced data bus system. In particular, such a system typically is formed of a twisted pair of wires enclosed within a shield.
In such a bus system, it is often difficult to isolate bus signal voltage component problems and the causes of possible distortions. Service technicians must be able to determine when a signal deviates from ideal, whether the problem is caused by the load, the source, the line, or a reflection. It is therefore a primary object of this invention to provide a coupler to aid in such discrimination.
Bus systems of the type described are also sensitive to common mode effects, that is, signals that are common to both balanced lines. Such signals can arise, for example, from RF induction or conductive effects. It is therefore a further object of this invention to provide a coupler of the type described which cancels the common mode signals.